Transparent plastic articles comprising certain polymeric components to provide temporary and reversible opacity characteristics

ABSTRACT

Unique transparent plastic (preferably though not necessarily polypropylene) articles that can be tailored to become opaque when exposed to a sufficiently high temperature and which returns to substantially the same transparency level upon cooling are provided. Such formulations include polymeric constituents that exhibit melting temperatures well below that for the majority clarified polypropylene, and thus which appear to become amorphous upon exposure to temperatures above such a lower melting temperature, thereby affecting the crystalline formation of the clarified polypropylene to the extent that opacity dominates the appearance thereof. Such lower melting temperature polymeric constituents include species such as low melt flow (up to 10) metallocene polyethylene and/or low density polyethylene, both of which exhibit melting temperatures of from about 60 to about 100° C., well below the typical polypropylene melting temperatures of roughly about 150° C. for homopolymer and about 165° for typical random copolymer. Preferably, as well, the melt flow for the polypropylene may be anywhere from about 1 to about 20, with the most preferable formulation comprising polyethylene and polypropylene components exhibiting similar melt flow properties (e.g., with a difference of at most 5 units) for better mixing results. Methods of producing such temperature sensitive transparent polypropylene formulations and articles are also encompassed within this invention.

FIELD OF THE INVENTION

This invention relates to unique transparent plastic (preferably, thoughnot necessarily polypropylene) articles that can be tailored to becomeopaque when exposed to a sufficiently high temperature and which returnto substantially the same transparency level upon cooling. Suchformulations include non-polypropylene polymeric constituents thatexhibit refractive index measurements similar to the base clarifiedpolypropylene at lower temperatures, as well as melting temperatureswell below that for the base clarified polypropylene. Upon exposure totemperatures in close proximity to the melting temperature of thenon-polypropylene polymeric constituents, the refractive index for suchconstituents will then become modified to the extent that the overallarticle appears at least partially opaque. In particular, thenon-polypropylene polymeric constituents should exhibit meltingtemperatures well below that for the base clarified polypropylene, fromabout 60 to about 100° C. (well below the typical polypropylene meltingtemperatures of roughly about 160-190° C. for homopolymer and about140-170° C. for typical random copolymer, both nucleated ornon-nucleated). In this manner, a temperature sensitivity measuringthermoplastic article may be provided, and may be tailored to specifictemperature ranges dependent on the melting temperatures exhibited bythe non-polypropylene polymeric constituents. Methods of measuringtemperature levels via the transformation of transparent polypropyleneformulations to at least partially opaque versions thereof are alsoencompassed within this invention.

BACKGROUND OF THE PRIOR ART

Clarified (a.k.a., transparent) polypropylenes have been utilized in avariety of end-use applications, including storage containers, medicaldevices, food packages, plastic tubes and pipes, shelving units, and thelike. Such base compositions, however, must exhibit certain physicalcharacteristics in order to permit widespread use. Uniformity inarrangement of crystals upon crystallization is a necessity to providean effective, durable, and versatile polypropylene article. In order toachieve such desirable physical properties, it has been known thatcertain compounds and compositions provide nucleation sites forpolypropylene crystal growth during molding or fabrication. Forclarification purposes, such crystals must exhibit very small sizes toreduce the haze within the target article. Generally, compositionscontaining such nucleating compounds crystallize at a much faster ratethan unnucleated polyolefin. Such crystallization at higher temperaturesresults in reduced fabrication cycle times and a variety of improvementsin physical properties, such as, as one example, stiffness.

Such compounds and compositions that provide faster and or higherpolymer crystallization temperatures are thus popularly known asnucleators. Such compounds are, as their name suggests, utilized toprovide nucleation sites for crystal growth during cooling of athermoplastic molten formulation. Generally, the presence of suchnucleation sites results in a larger number of smaller crystals. As aresult of the smaller crystals formed therein, clarification of thetarget thermoplastic may also be achieved, although excellent clarity isnot always a result. The more uniform, and preferably smaller, thecrystal size, the less light is scattered, as alluded to above. In sucha manner, the clarity of the thermoplastic article itself can beimproved. Such clarified polypropylenes are well known within thepolyolefin industry and pertinent art to that effect is noted below.

Polyethylenes have been added to such clarified polypropylenes in thepast in order to provide improvements in impact resistance, sometimeswith very little detrimental effect on the haze characteristics thereof.However, in the past, such polyethylene additives have exhibitedproblematic high temperature opacifying properties thereby compromisingthe clarified polypropylene for certain end-uses. In particular, the lowamount of impact resistance-improving polyethylenes provide amorphouscharacteristics upon exposure to sufficient heat, again therebyaffecting the transparent nature of the target article. To date, such aproblem has remained as such an undesirable issue within such polymerarticles. Nowhere in the prior art has this phenomenon been furtherstudied and improved upon for the purpose of utilizing such a pastproblem for certain benefits. It is the direction of this invention toinvestigate the possibilities of modifying such transparentpolypropylene formulations into unexpectedly effective temperatureindicators for certain end-uses.

Such an opacifying problem in the past is generally associated with therefractive index measurements of the component plastic phases within theparticular article. When approaching or reaching the target plasticsmelting temperature, a sudden change in refractive index occurs. In thepast, as noted above, it was noticed that certain blends of differentplastics (such as the aforementioned polypropylene includingstrength-enhancing amounts of polyethylene) having similar refractiveindices at room temperature will appear transparent, at least to somedegree in visible light. Any sufficient modification of the refractiveindex differences between such blended plastics will result in thescattering of light at the boundary (or boundaries) of the differentphases of plastic components. Such a sudden change may be caused byexposure to higher temperatures (e.g., a temperature high enough tocause at least partial melting of one the plastic phases therein),thereby causing an increase in light scattering within the targettransparent article. In such an instance, the target article will thenappear opaque.

In the past, such an opacification problem has proven detrimental as theconsumer needs for such articles relies on retained transparency, ratherthan low temperature generation of opaque characteristics. However, ithas now been determined that such a past problem can be controlled andtailored to a certain level in order to provide beneficial temperaturesensing abilities in an effort to provide a safer, simplified guide tothe consumer as to the temperature level exhibited by a target liquid,foodstuff, or other item contained within such a transparent targetplastic article, or surface to which a transparent target plasticarticle is contacted. Such a development is not simple to achieve as theselection of proper non-polypropylene polymeric constituent(s) havingthe necessary room temperature refractive index levels similar to thebase polypropylene, as well as the proper range of melting temperaturesto provide sufficient opacity indications of temperature levels requiresextensive consideration of different potential additives of this type,particularly to permit a return to substantially the same roomtemperature transparency level after exposure to sufficiently hightemperatures to effectuate the opacity indications needed for such atemperature sensing method. Considering the desire to avoid utilizationof mercury- or solvent-based thermometers, and the continued interest inprotecting consumers from high temperature food and drink items (e.g.,microwaveable food, hot coffee, and the like), such a simplified andsafe temperature sensing method is desirable.

OBJECTS AND DESCRIPTION OF THE INVENTION

Therefore, an object of the invention is to provide a clarifiedpolypropylene formulation or article that exhibits opacifying propertiesupon exposure to a temperature between 60 and 100° C. in order toprovide a temperature indicating system with such a particularpolypropylene formulation or article. Another object of this inventionis to provide an end-use article that indicates exposure to specifictemperatures upon exposure to uncertain heat sources. Also, theinventive polypropylene formulations or articles exhibit reversibletransparency properties upon cooling subsequent to exposure tosufficiently high temperatures for opacification.

Accordingly, this invention encompasses a clarified polypropylenearticle comprising at least one base polypropylene component and atleast one separate non-polypropylene polymeric additive mixed thoroughlytherein, wherein said separate polymeric additive exhibits a refractiveindex at room temperature (e.g., from about 20-30° C.), substantiallysimilar to the refractive index of said at least polypropylene component(e.g., within about +/−0.005 refractive units, at most, from that ofsaid polypropylene, preferably at most +/−0.003, and most preferably, atmost +/−0.001), and wherein said at least polypropylene componentexhibits a melting temperature of at least 140° C., and therein saidnon-polypropylene polymeric additive exhibits a melting temperature inthe range of from about 60° to about 100° C., more preferably betweenabout 65 and 95° C., and most preferably between about 70 and 95° C.Also encompassed within this invention is a method of sensing atemperature change between the temperatures of from about 60° to about100° C., more preferably between about 65 and 95° C., and mostpreferably between about 70 and 95° C., comprising the steps ofproviding such a plastic article as defined above, subjecting it to anexternal temperature, and empirically viewing said heated plasticarticle to determine a change in transparency therein. Any degree ofopacification will indicate exposure to temperatures in excess of thelower temperature in the range for sensing capacity noted above. Thus,this invention further encompasses a clarified polypropylene formulationthat exhibits a haze of at most 20 (which may be glossy or matte infinish) when exposed to a temperature below 40° C., but when exposed toa heating temperature of at least 60° C., becomes opacified, and whichretains substantially the same initial haze upon cooling to atemperature below 40° C.

Such a composition may actually comprise any clear plastic that includesa certain amount of a separate polymeric additive that initiallyexhibits a refractive index substantially similar to that of the clearplastic majority component (such as polypropylene, polyacrylate,polystyrene, polycarbonate, and the like). Thus, upon exposure tosufficiently high temperatures the refractive index of the separatepolymeric additive will modify to the extent that the plastic appearsopaque to at least a noticeable degree. Although polypropylene is thepreferred base plastic component for such purposes, again, other typesmay be utilized as long as the opaque result is available at atemperature below the melting and/or heat distortion temperature of thebase plastic component itself.

As alluded to above, the polypropylene article may be finished in anymanner, such as high-gloss, matte, or other type, to provide a low-hazearticle (but not necessarily a clarified article). In such manner, then,the opacification step may simply increase the haziness present therein(or likewise, dramatically reduce the clarity thereof).

The separate polymeric additive is a material that exhibits a changefrom crystalline to amorphous state upon exposure to temperatures belowthe melting temperature of the necessary clarified polypropylenecomponent (as noted throughout between about 140 and 190° C., as oneexample). In such a situation, there would be a phase transition betweenthese two states for the separate polymeric additive that alters therefractive index of the material itself. This refractive index changemust exceed about 0.003 from that of the clarified polypropylenecomponent (which is not altered to any substantial degree upon exposureto such elevated temperatures (due to the retention of the crystallinephase for the polypropylene) in order to provide the desired temperaturesensitivity capacity. Thus, the separate polymeric additive shouldexhibit a refractive index change upon exposure to such elevatedtemperatures of at least 0.003, more preferably between 0.003 to 0.010,and most preferably between about 0.003 to 0.005, all in comparison withthe refractive index exhibited by the clarified polypropylene componentat the same elevated temperatures.

Preferably, though not required, the separate polymeric additive apolyethylene from the general class of metallocene polyethylenes, lowdensity polyethylenes, linear low density polyethylenes, and anymixtures thereof, and is present in any amount as long as thepolypropylene constitutes the majority of the article's composition andthe haze of the article at a wall thickness of at most 1 mm, is lessthan about 20, more preferably below about 15, and most preferably belowabout 11. Other types of polymeric additives may be utilized as well forthis purpose, including certain sterically hindered polymers thatexhibit such a change in refractive index upon exposure to such elevatedtemperatures (e.g., the glass transition temperature for the separatepolymeric additive). Furthermore, the separate polymeric additive isalso preferably present in an amount of from about 5 to 35% by weight ofthe total article, more preferably from about 10 to 30%, and mostpreferably from about 20 to about 30%. In such a manner, the overallmelting temperature of the article is not significantly lowered from themelting temperature of the polypropylene constituent (although,invariably some lowering of such a temperature will occur when a lowermelting temperature, such as the separate polymeric additive, is addedin appreciable amounts). Such an article will thus not easily deformfrom its intended shape at temperatures just above that required foropacification.

Alternatively, then, the invention further encompasses a clarifiedpolypropylene formulation that exhibits a haze of at most 20 (at 1 mm orless wall thicknesses with a suitable finish, as previously discussed)when exposed to a temperature below 40° C., but when exposed to atemperature of at least 60, preferably at least 65, more preferably atleast 70, and most preferably at least 72° C. (with some preferredembodiments including temperatures as high as in excess of 90° C.),becomes opacified (e.g., a haze of above 55, preferably above 60, morepreferably above 70, and most preferably above 75), and which retainssubstantially the same initial haze (e.g., within +0.5% haze unitsdifference) upon cooling to a temperature below 40° C. Additionally,this invention concerns the method of producing such specific clarifiedheat-sensitive polypropylene articles.

The most effective clarifying agent known to the industry and availablecommercially at this time is also a type of nucleator, namelydibenzylidene sorbitol acetal derivative compounds (again, “DBS”). Suchcompounds are typical nucleator compounds, particularly forpolypropylene end-products, and include, without limitation, compoundssuch as 1,3-O-2,4-bis(3,4-dimethylbenzylidene) sorbitol, available fromMilliken Chemical under the trade name MILLAD® 3988-brand clarifyingagents (hereinafter referred to as 3,4-DMDBS),1,3-O-2,4-bis(p-methylbenzylidene) sorbitol, also available fromMilliken & Company under the trade name MILLAD® 3940-brand clarifyingagents (hereinafter referred to as p-MDBS). Again, such compoundsprovide excellent clarification and relatively effective nucleationcharacteristics for target polypropylenes and other polyolefins. Otherpolypropylene clarifiers do exist, but none to the effect of such DBStypes. In any event, such clarified (transparent) polypropylenes asrequired within this invention require the presence of at least oneclarifying agent, preferably DBS types, and most preferably 3,4-DMDBS inorder to provide the necessary level of low haze (20% or lower;preferably, 15% or lower; and most preferably, about 11% or lower in atmost 1 mm wall thickness parts).

For thin parts (e.g., 10 mils of less in thickness), the clarifierpresent within the target PP may be sodium2,2′-methylene-bis-(4,6-di-tert-butylphenyl) phosphate (from Asahi DenkaKogyo K.K., known as and hereinafter referred to as NA-11), aluminumbis[2,2′-methylene-bis-(4,6-di-tert-butylphenyl)phosphate] with lithiummyristate (also from Asahi Denka Kogyo K.K., which is understood to beknown as and hereinafter referred to as NA-21), or other nucleators,particularly those which provide extremely quick crystal formationand/or arrangement (since thin parts merely require fast nucleation forclarification). Such additives provide the desired low haze propertieswithin such thin parts for the aforestated reasons.

The additives needed to impart the reversible opacifying effects notedabove must be polymeric in nature, exhibit a melting point of at least40° C. (preferably, at least 50° C.) lower than that of thepolypropylene constituent, become amorphous upon exposure to its meltingtemperature, and return to its original crystal structure upon coolingbelow its melting temperature to the extent that the retained haze ofthe entire formulation or article is modified by at most 0.5 haze unitsover the initial haze measurement. In order to achieve this result,again, the polymeric additives must exhibit similar refractive indicesto the base polypropylene(s) at room temperature (at least). Uponexposure to sufficient heat, as noted above, the refractive index of thepolymeric additive(s) must become modified significantly from that ofthe polypropylene (e.g., in excess of at least 0.003 units, as ntoedabove).

Certain polyethylene additives can be added to such clarifiedpolypropylene formulations (such polyethylenes are actually mixed withinthe molten resin prior to cooling and molding and not added to thealready molded article) such a purpose, provided they meet certainrequirements in terms of miscibility with the polypropylene (and thusuniformity of appearance, and the like, after production, duringopacification, and return to transparency). Thus, the melt flow index ofthe desired polyethylene must be from about 0.5 to about 100, and themelt flow index of the polypropylene must be within the same range [aspreferably, though not necessarily, measured under similar conditions,namely, at least, similar characteristics such as densities, a RockwellHardnesses (R scale), a tensile strengths, elongations at yield,flexural moduli, Izod impact strengths, and deflection temperatures].Preferably, the melt flow index of the two components are within 5 unitsof each other, again to best ensure thorough mixing and thus properfunctioning as intended.

As noted above, polyethylenes have been added in the past topolypropylene formulations (clarified or otherwise) for the purposes ofincreasing impact resistance properties. However, in some instances thepresence of such a different crystalline structure within the clarifiedpolymer creates too great a difference in refractive index initially(e.g., at room temperature), thereby causing too great an increase inhaze initially (to above the threshold of 20%, preferably above 15%, andmost preferably above 11% in 1 mm at most wall thickness parts), priorto any exposure to elevated temperatures. Thus, as aforementioned, theproper polyethylenes to be selected for this purpose must not cause sucha severe haze increase in such a manner. Furthermore, such priorpolypropylene additions of polyethylene have not required the presenceof low melt flow (or low melting point) polyethylene components toprovide the targeted temperature sensitivities herein desired. In anyevent, there have been no attempts to harness this previous problematiccharacteristic for the benefits now realized (specific, thermosensitiveproperties).

The properly selected polyethylenes, if polyethylenes are utilized, havethus more preferably been determined to be from two general classes:namely, metallocene polyethylenes (hereinafter “mPE”), linear lowdensity polyethylenes (hereinafter “LLDPE”), and low densitypolyethylenes (hereinafter “LDPE”; polyethylene itself will hereinafterbe designated as “PE” and polypropylene as “PP”, which indicatesclarified PP as well). Such specific classes of PE, when possessing theproper melt flow index in the range required above, provide thenecessary characteristics in terms of low haze effects within PP, thelow melting point in comparison with PP (in the range of between 70 and100° C.), the reversible transfiguration from crystalline structure toamorphous state and back to nearly identical crystalline structure uponexposure to heat and then subsequent cooling, and, just as important,the lack of modification of the physical properties of the PP-dominatedformulation or article such that the PP can be utilized for myriadend-uses just as regular (e.g., non-PE added) PP has been utilized inthe past (particularly in terms of clarified PP end-uses).

Examples of such properly selected PE additives include, withoutlimitation, EXACT® 2M004, 2M009, and 2M011-brand polymer additives withmelting points of 90, 72, and 72° C., respectively and and melt flowindices (MFIs) of 3, 10, and 1, respectively, all from ExxonMobil. Aspecific LDPE example meeting this criteria includes, again, withoutlimitation, BOREALIS® OE5620-brand polyethylene and a specificnon-limiting LLDPE (linear low density polyethylene) example includesDOWLEX® 2552-E-brand polyethylene. Other types of such PE additives (aswell as other polymeric additives) that provide the desired inventiveeffects should be well within the purview of the ordinarily skilledartisan as such additives must provide the desired properties discussedin detail above. High density polyethylene (HDPE) is an example of aclass of PE that does not meet the current requirements due tosiginicant haze development at room temperature caused by thesignificant difference in refractive indices with PP, particulalrywithin the target PP article after cooling subsequent to exposure tosufficient heat to provide opacification. Thus, the selection criteriais difficult to accomplish, although relatively simple to determine,particularly for the range of temperatures for which exposure causes thedesired PP opacification.

The properties of ultimate target PP formulation or articles should berelatively the same as those for any standard PP formulation or article(and thus the PE additive does not deleteriously affect thecharacteristics thereof). Thus, relatively high polymer crystallizationtemperature (for ease in and/or quickness of production), good clarity,compatibility with standard additives (acid scavengers, lubricants,antioxidants, colorants, and the like), surface texture, adhesion tomolds or other production machinery, pumpability of the molten resin(not too high viscosity), should not be altered to any great extentthrough the addition of the opacifying additive. Again, the classes ofPE additives noted above should function in this capacity, althoughother classes should also provide such results as well.

Thus, it has been found that a clarified PP formulation or articleexhibiting a haze of at most 20% (again, within at most 1 mm thicknessparts), and comprising a composition of from 65-95% by weight of PP(plus additives, as discussed below), and from 5-35% of a temperaturesensitive opacifying additive having a melt flow between 0.5 and 100, amelting temperature between about 60 and 100° C., and the ability totransform from a crystalline structure to an amorphous structure uponexposure to its melting temperature, thereby modifying its refractiveindex to a level disparate from that of the base polypropylene, andreturn to its original crystalline structure upon cooling to below it smelting temperature, to the effect that the overall formulation orarticle exhibits a subsequent haze of at most +0.5% different than theinitial haze measurement, is provided by the invention as describedherein.

Such a combination of PP and additive (e.g., mPE or LDPE as noted above)may be incorporated within an additives package composition includingother components, including, the base PP, the additive, and othercompounds and formulations noted below in greater detail. Such aninventive combination, and compositions comprising such an inventivecombination, may be present in any type of standard polyolefin additiveform, including, without limitation, powder, prill, agglomerate, liquidsuspension, and the like. Basically, any form may be exhibited by such acombination or composition including such combination made fromblending, agglomeration, compaction, and/or extrusion. The totalconcentration of the inventive combination of PP and additive ispreferably from about 70-95% PP (and other standard compounds) and fromabout 5-30% additive; more preferably about 75-90% PP and the remainderthe additive and most preferably from about 80-90% PP and the remainderthe additive (e.g., 20-30%). The standard compounds alluded to aboveinclude, without limitation, different types of commonly addedantistatic agents, colorants, antioxidants, acid scavengers, colorants,antimicrobials, plasticizers, stabilizers, ultraviolet absorbers,perfumes, organoleptic improvement additives, and other similar standardPP thermoplastic additives. Other additives may also be present withinthis composition, most notably antioxidants, antistatic compounds,perfumes, acid netutralizers, and the like. The term “organolepticimprovement additive” is intended to encompass such compounds andformulations as antioxidants (to prevent degradation of both thepolyolefin and possibly the present 3,4-DMDBS and/or MDBS or other likecompounds), acid neutralizers (to prevent the ability of appreciableamounts of residual acids or catalysts from attacking the clarifying orother agents), and benzaldehyde scavengers (such as hydrazides,hydrazines, and the like, to prevent the migration of foul tasting andsmelling benzaldehydes to the target PP surface, if benzaldehyde-basedclarifiers are utilized). Such compounds and formulations can be addedin any amounts in order to provide such organoleptic improvements asneeded. However, the amounts should not appreciably affect the hazeresults for the target PP itself. Thus, lower amounts on the order offrom about 20 ppm to about 4,000 ppm of the total PP component aredesired.

The clarified, heat-sensitive PP is intended to be utilized as, forinstance and not by limitation, any end-use in which temperatureindication of a clarified PP is desired. Thus, against as non-limitingintended uses, reheatable food containers (such as microwaveable storagecontainers for refrigerator use, as an indication that sufficientheating has taken place upon reheating of the foodstuff stored therein);baby bottles (as an indication that the temperature of the liquidtherein is too hot for ingestion by the target child); PP baby foodcontainers (to facilitate heating of the foodstuff contained therein insuch a manner as to indicate if the heating temperature is too high forserving to the target child; furthermore, upon return to a clarifiedstate, the indicator shows proper serving temperature as well); certainwindows, such as for saunas, and the like, that indicate too hightemperatures upon opacification; laboratory flasks, and the like, again,as an indication that the temperatures of such labware are excessive forcertain reactions or storage conditions, or the like; strips of articlesfor attachment to machinery parts as quick indicators of suitable orunsuitable temperature generations (such as, without limitation,placement on automobile radiators as indicators of the propertemperature range exhibited by such an engine part); basically, again,any end-use in which temperature indication through a simple(reversible) opacification characteristic is needed or desired.

Preferred Embodiments of the Invention

Examples of particularly preferred clarified PP formulations or articlescomprising such temperature-sensitive additives and thus exhibiting thedesired low temperature controlled reversible opacifying characteristicsare presented below.

Production of Inventive PP Mixtures

The specific PP mixtures were comprised of flake PP, for these purposesrandom copolymer (RCP) PP was utilized, either Basell Novolen® 3240 NCresin or Borealis RB 307 MO resin, with MFIs of 12 and 1.5,respectively, and melting temperatures of about 182 and 165° C.,respectively. To this flake PP was added a powder of 3,4-DMDBS (about2500 ppm), and other compounds, as noted below. Three types of PE werealso mixed, individually, into different PP formulations at threedifferent concentrations (10%, 20%, and 30% of the total weight of thearticle; one PE with each different PP noted above), namely Exact®2M004, 2M009 and 2M011 mPE additives. Control clarified PP articles werealso produced having no separate polymeric additive (e.g., mPE) present.

One kilogram batches of target polypropylene were thus produced inaccordance with the following table:

POLYPROPYLENE COMPOSITION TABLE Component Amount Polypropylene RCP flake(noted above) to 1,000 g Irganox ® B215 Antioxidant (from Ciba Specialty1500 ppm Chemicals) Calcium Stearate, Acid Scavenger 800 ppm 3,4-DMDBS2500 ppm Separate Polymeric Additive (as noted below) as noted below

The base RCP PP resin and all additives, including the separatepolymeric additive, were weighed and then blended in a Papenmeier(Welex) high-intensity mixer for 1 minute at about 1600 rpm. All sampleswere then melt compounded on a Killion single screw extruder at a rampedtemperature from about 204° to 232° C. through four heating zones. Themelt temperature upon exit of the extruder die was about 246° C. Thescrew had a diameter of 25 mm and a length/diameter ratio of 24:1. Uponmelting the molten polymer was filtered through a 60 mesh (250 micron)screen. Plaques of the target polypropylene were then made on an Arburg25 ton injection molder. The molder barrel was set at a temperature of220° C. The plaques had dimensions of about 50 mm×70 mm×1.00 mm madefrom a mirror-polished mold (SPI 1). The mold cooling circulating waterwas controlled at a temperature of 25° C. After allowing the plaques toage for 24 hours at room temperature, haze values were measuredaccording to ASTM Standard Test Method D1003-61 “Standard Test Methodfor Haze and Luminous Transmittance of Transparent Plastics” using a BYKGardner Hazegard Plus.

The specific trial articles produced thereby are listed below in termsof the type and amount of separate polymeric additive present within thestandard HP composition listed above in the TABLE (comprising the BasellPP formulation):

SPECIFIC HP FORMULATION COMPOSITION TABLE Formulation # mPE AdditiveAmount Present 1 EXACT ® 2M004 10% by weight 2 EXACT ® 2M004 20% byweight 3 EXACT ® 2M004 30% by weight 4 EXACT ® 2M011 10% by weight 5EXACT ® 2M011 30% by weight

These plaques were then subjected to heating in an oven to analyze theopacification properties and clarification retention propertiestherefor. Each plaque noted below was placed in a standard laboratoryoven heated at a set temperature, as noted:

EXPERIMENTAL TABLE 1 Opacification Properties for Inventive Formulations(Plaques) at Different Temperatures Exposure Temperature Form. # (roomor oven) Empirical Appearance. 1 Room (˜30° C.) Clear 4 Room (˜30° C.)Clear 5 Room (˜30° C.) Clear Control Room (˜30° C.) Clear 4 Oven (81°C.) Opaque (very hazy) 5 Oven (81° C.) Opaque (more hazy than 4) ControlOven (81° C.) Clear 1 Oven (107° C.) Opaque (very hazy) 4 Oven (107° C.)Opaque (very hazy; same as 1) 5 Oven (107° C.) Opaque (same as 1 and 4)Control Oven (107° C.) Clear

Upon cooling room temperature again, the 1, 4, and 5, sample plaques allreturned to their initial clear appearance with no residual appreciablehaze increases empirically noticeable. Thus, the inventive plaquesaccord excellent temperature sensitivity and provide effectiveindications of specific temperature exposures.

Formulations (plaques) 1, 2, and 3, from above, were then also tested tothis high oven temperature of 107° C. and then quickly removed andcooled to room temperature. The haze at different times after coolingcommenced were measured, indicating the rate at which cooling occurredin terms of return to initial haze measurements (as well astransformation of the mPE from amorphous state to crystalline state).The measurements were as follows:

EXPERIMENTAL TABLE 2 Haze As A Function Of Cooling Time And QuicklyLowering Temperature Form # (Init. Haze) Cooling Time (seconds) HazeMeasurement (%) 1 (˜11%) 10 ˜56 1 20 ˜32 1 60 ˜18 2 (˜12%) 10 ˜72 2 20˜40 2 60 ˜21 3 (˜15%) 10 ˜77 3 20 ˜57 3 60 ˜23 Control (˜7%) 10 ˜7Control 20 ˜7 Control 60 ˜7

Thus, the inventive articles can be tailored not only to show certaintemperature levels, but also can be tailored to show the reduction inhigh temperature in terms of clarity retention after a cetain amount oftime subsequent to such high temperature exposure, and yet also betransparent in nature and not lose such clarity characteristics aftertemperature indication is accomplished. Furthermore, such inventivearticles may be utilized repeatedly for such temperature sensingpurposes as long as opacification of the target article can easily beempirically determined.

Having described the invention in detail it is obvious that one skilledin the art will be able to make variations and modifications theretowithout departing from the scope of the present invention. Accordingly,the scope of the present invention should be determined only by theclaims appended hereto.

That which is claimed is:
 1. A clarified temperature-sensingpolypropylene article exhibiting walls of preselected thicknesses andcomprising at least one base polypropylene component, at least oneclarifying agent, and at least one separate non-polypropylene polymericadditive mixed thoroughly therein, wherein said article is transparent,wherein said at least one polypropylene component exhibits a meltingtemperature of at least 140° C., wherein said at least onenon-polypropylene polymeric additive exhibits a melting temperature inthe range of from about 60° to about 100° C., and wherein said at leastone separate non-polypropylene polymeric additive is present in anamount to effectuate an opaque appearance to said article upon exposureto temperatures above the melting temperature of said additive and belowthe melting temperature of said polypropylene component and to permitsaid article to return to a transparent appearance upon subsequentreduction of the temperature to which said opaque article is exposed toa temperature below the melting point of said non-polypropylenepolymeric additive, wherein the effectuation of such an opaqueappearance indicates exposure to a temperature above the melting pointof said non-polypropylene polymeric additive.
 2. The polypropylenearticle of claim 1 wherein said at least one separate polymeric additiveexhibits a melting temperature of between about 65 and 95° C.
 3. Thepolypropylene article of claim 2 wherein said at least one separatepolymeric additive exhibits a melting temperature of between about 70and 95° C.
 4. The polypropylene article of claim 1 wherein said at leastone separate polymeric additive is a polyethylene.
 5. The polypropylenearticle of claim 4 wherein said polyethylene is selected from the groupconsisting of metallocene polyethylenes and low density polyethylenes.6. The polypropylene article of claim 5 wherein said polyethylene is ametallocene polyethylene.
 7. The polypropylene article of claim 1wherein said separate polymeric additive is present in an amount of fromabout 5 to about 35% of the total weight of the article.
 8. Thepolypropylene article of claim 7 wherein said separate polymericadditive is present in an amount of from about 10 to about 30% of thetotal weight of the article.
 9. The polypropylene article of claim 8wherein said separate polymeric additive is present in an amount of fromabout 20 to about 30% of the total weight of the article.
 10. Aclarified polypropylene article having walls of at most about 1 mm inthickness, wherein said article exhibits a haze of at most 20 whenexposed to a temperature below 40° C., but when exposed to a heatingtemperature of at least 60° C., becomes opacified, and which retainssubstantially the same initial haze upon cooling to a temperature below40° C., wherein said clarified polypropylene article comprises at leastone clarifying agent therein.
 11. The polypropylene formulation of claim10 wherein the initial haze of said article is at most
 15. 12. Thepolypropylene formulation of claim 11 wherein the initial haze of saidarticle is at most
 11. 13. The polypropylene formulation of claim 10wherein said heating temperature is at least 65° C., and the haze ofsaid formulation at said heating temperature is at least 55%.
 14. Thepolypropylene formulation of claim 13 wherein said heating temperatureis at least 70° C.
 15. The polypropylene formulation of claim 13 whereinsaid heating temperature is at least 72° C.
 16. The polypropyleneformulation of claim 13 wherein said heating temperature is at least 90°C.